JP4897334B2 - Surface inspection method and surface inspection apparatus - Google Patents

Description

  The present invention relates to a surface inspection method and a surface inspection apparatus for detecting fine scratches and foreign matters on a substrate surface such as a semiconductor wafer.

  Conventionally, when detecting fine foreign matter or fine scratches attached to the surface, a foreign object or scratch is detected by irradiating the inspection surface with a laser beam and detecting scattered light from the foreign matter or scratches. It was.

  FIG. 8 shows an outline of the surface inspection apparatus, and shows a silicon wafer 1 as an object to be inspected.

  The silicon wafer 1 is held in a horizontal posture by a substrate chuck 2, and the substrate chuck 2 is rotated by a motor 3 at a predetermined rotational speed.

  An inspection light irradiation system 5 and a scattered light receiving system 6 are provided on the inspection surface 4 of the silicon wafer 1, and the inspection light irradiation system 5 is provided with inspection light from a light source unit, for example, a laser beam 7 on the inspection surface 4. Is reflected at a required incident angle, and the reflected light 7 ′ reflected by the inspection surface 4 is detected by the reflected light detector 8. The light intensity of the reflected light 7 ′ of the laser beam 7 detected by the reflected light detector 8 is fed back to make the irradiation intensity of the laser beam 7 constant.

  The scattered light receiving system 6 has an optical axis that intersects the optical axis of the inspection light irradiation system 5, and a side scattered light detector 9 and a forward scattered light detector 11 are provided on the optical axis. The side scattered light detector 9 and the forward scattered light detector 11 are different in the intersecting direction and the intersecting angle. The side scattered light detector 9 and the forward scattered light detector 11 detect light scattered by the laser beam 7 hitting a foreign object or scratch.

  The inspection surface 4 is inspected by rotating the inspection surface 4 in the radial direction of the silicon wafer 1 at a predetermined pitch (predetermined speed) by rotating the motor 3 with the laser beam 7 applied to the inspection surface 4. Move. The irradiation point of the laser beam 7 moves in the radial direction while rotating to scan the entire inspection surface 4. When the laser beam 7 passes through a foreign object or scratch, reflected light is scattered, and the side scattered light detector 9 and the forward scattered light detector 11 receive the scattered light 12.

  The received scattered light 12 is converted into an electrical signal by a photoelectric conversion element, further amplified by an amplifier, processed as a foreign matter signal, and stored as a test result in a required storage device.

  An example of output signals of the side scattered light detector 9 and the forward scattered light detector 11 is shown in FIG. Normally, the output signal includes a signal component S and a DC component D, and the inspection surface 4 is an even smooth surface that is polished. When the inspection surface 4 is rough and the scattering reflection of the inspection surface 4 itself is large, a large amount of direct current component D appears.

  Next, FIG. 10 shows the relationship between the detected light intensity and the signal output level when the side scattered light detector 9 and the forward scattered light detector 11 receive light. The output level is proportional to the curve A in FIG. 10, and when the detected light intensity exceeds a predetermined value and the signal output level reaches the proportional limit (measurement limit), the output signal is not linear. , Become saturated. Therefore, the range I maintaining the proportional relationship is the measurement range (dynamic range) of the detector.

  However, when the inspection surface 4 is a rough surface (wafer back surface) or a wafer surface on which a metal film is generated, irregular reflection on the surface itself increases, and the direct current component D shown in FIG. It is conceivable that the light intensity exceeds the measurement range, and substantial measurement cannot be performed.

  For this reason, as a method of expanding the measurement range, there is a method of logarithmic amplification using a logarithmic amplifier. The signal output level when amplified using a logarithmic amplifier is shown by curve B in FIG.

  In the case of logarithmic amplification, as can be seen from comparison between curve A and curve B, the increase rate of the signal level decreases as the detected light intensity increases, and the detected light intensity increases by IA until the measurement limit is reached. That is, the measurement range is expanded by IA.

  However, when logarithmic amplification is performed, an output signal having a low detection light intensity is emphasized. For example, when the light intensity is P, the curve B has a signal output level that is larger by ΔS than the curve A, and therefore, low level noise is perceived greatly, and the S / N ratio tends to decrease. Further, when the detection signal band is a high frequency, the logarithmic amplifier is required to have a high S / N ratio and high responsiveness, and is expensive.

  In addition, there exist some which are shown by patent document 1 as a surface inspection apparatus, and there are some which are shown by patent document 2 and nonpatent literature 1 as what expands a dynamic range by logarithmic amplification.

JP 2004-271519 A

JP 2005-526239 A

Supervised by Shinya Fujita, edited by Kei Kawada, “Theory and Practice of New Optical Microscope (Volume 1) Laser Microscope”, Interdisciplinary Planning, Inc., March 28, 1995, p. 116

  In view of such circumstances, the present invention provides a surface inspection method and a surface inspection apparatus that have a simple configuration and a wide dynamic range, and can perform surface inspection with a high S / N ratio even when the inspection surface itself has a large amount of scattered light. It is to provide.

  The present invention provides a surface inspection method in which a laser beam is irradiated and scanned on an inspection surface to detect foreign matter or the like on the inspection surface, and the laser beam irradiation site is divided into a required number of detection regions, In order to change the detected light intensity, the receiver receives the light and obtains the required number of output signals with different detected light intensities for the examination site. Of the required number of output signals, the output signal indicates the maximum value that is not saturated. Is selected as the surface inspection signal, and the laser beam is irradiated so that the light intensity distribution changes at the irradiated part, and the required number of detection areas are set so that the detected light intensity is different. In addition, the present invention relates to a surface inspection method in which the amount of light is adjusted by an optical filter so that the detection light intensity differs between detection regions.

  The present invention also provides an inspection light irradiation system for irradiating the inspection surface with a laser beam, a scattered light receiving system for detecting scattered light, and an arithmetic processing for detecting foreign matter based on the scattered light detection output of the scattered light receiving system. And the scattered light receiving system divides the laser beam irradiation part into a required number of detection areas, and detects the detection light so that the intensity of the scattered light received varies between the detection areas. Then, the arithmetic unit selects the scattered light detection output of the maximum value that is not saturated among the plurality of scattered light detection outputs obtained for the same part as the surface inspection signal, and inspects foreign matter or the like based on the surface inspection signal. The inspection light irradiation system irradiates the laser beam so as to obtain a light intensity distribution in which the light intensity changes at the irradiated part, and the inspection region is set so that the detected light intensity is different. Related surface inspection equipment, and also Serial scattered light receiving system, the detected light intensity is different as between the examination region, but according to the surface inspection apparatus in which the optical filter is provided.

  According to the present invention, in the surface inspection method for detecting a foreign matter or the like on the inspection surface by irradiating and scanning the inspection surface with a laser beam, the laser beam irradiation site is divided into a required number of detection regions, and each detection is performed. The receiver receives light so that the detected light intensity varies between regions, and obtains the required number of output signals with different detected light intensities for the examination site, and shows the maximum value that is not saturated among the required number of output signals. Since the output signal is selected as the surface inspection signal, the dynamic range of the scattered light detection can be expanded with a simple configuration without changing the configuration of the device as before, and the scattered light detection with a large S / N ratio is possible. To do.

  Furthermore, according to the present invention, the inspection light irradiation system for irradiating the inspection surface with a laser beam, the scattered light receiving system for detecting scattered light, and the detection of foreign matter based on the scattered light detection output of the scattered light receiving system. And the scattered light receiving system divides the laser beam irradiation area into a required number of detection areas, and detects the scattered light intensity received between the detection areas. The light is detected, and the arithmetic unit selects a scattered light detection output of the maximum value that is not saturated among a plurality of scattered light detection outputs obtained for the same part as a surface inspection signal, and a foreign object or the like based on the surface inspection signal. Therefore, it is possible to expand the dynamic range of scattered light detection with a simple configuration without changing the device configuration from the conventional one, and to enable detection of scattered light with a large S / N ratio. Show the effect

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  A first embodiment of a surface inspection method according to the present invention will be described with reference to FIGS.

  The basic configuration of the surface inspection apparatus for performing the surface inspection method according to the present invention is the same as that shown in FIG. In FIG. 8, the surface inspection by the side scattered light detector 9 and the forward scattered light detector 11 is performed in the same manner. Therefore, the surface inspection by the side scattered light detector 9 will be described below with reference to FIG. A case where the above is performed will be described.

  As shown in FIG. 1, the cross section of the light beam that the laser beam 7 emitted from the inspection light irradiation system 5 irradiates the inspection surface 4 has an elliptical shape, and the long diameter is orthogonal to the beam scanning direction, that is, the silicon wafer 1. The rotation direction R is perpendicular to the rotation direction R. The required number of light receiving areas of the side scattered light detector 9 is set in the major axis direction (beam feeding direction Q), and four detection areas of CH1, CH2, CH3, and CH4 in the figure are set, and each detection area is independent. Light reception is possible. The detection areas are adjacent to each other, and the pitch between the detection areas is equal to the distance (feed pitch p) that the beam moves in the radial direction when the silicon wafer 1 rotates once.

  Further, the irradiation light intensity distribution at the point irradiated with the laser beam 7 has, for example, a distribution having a peak at the head side in the beam feeding direction and gradually decreasing toward the rear.

  Therefore, under the same reflection conditions when the laser beam 7 is irradiated, the detected light intensities S1, S2, S3, S4 corresponding to the respective detection regions CH1, CH2, CH3, CH4 are S1> S2> S3> S4. If the ratio of detected light intensities is S1: S2: S3: S4 = α: β: γ: δ, the relationship between the detected light intensities S1, S2, S3, S4 and the signal output level is shown in FIG. As shown in

  In the figure, the vertical axis I indicates the detected light intensity when detection is performed in the detection region CH1, and L indicates the proportional limit (measurement limit) between the detected light intensity I and the output signal level S.

  The surface inspection is performed by irradiating the inspection surface 4 with the laser beam 7 shown in FIG. 1, rotating the silicon wafer 1 at a predetermined constant speed, and further moving the silicon wafer 1 at a predetermined constant speed in the radial direction. Let As described above, the moving speed of the silicon wafer 1 is set so that the laser beam 7 is sent in the radial direction at the feed pitch p.

  When the laser beam 7 is scanned over the entire inspection surface 4, each of the detection regions CH1, CH2, CH3, and CH4 scans the entire inspection surface 4. That is, the inspection surface 4 is scanned four times by the detection areas CH1, CH2, CH3, and CH4.

  When the silicon wafer 1 is rotated at a constant speed and the silicon wafer 1 is moved at a constant speed, the moving time of the feed pitch p becomes constant at Δt. The state is replaced with the detection area on the head side. For example, with reference to the state of FIG. 1, CH2 moves to the position of CH1 after Δt, CH3 moves to the position of CH1 after 2Δt, and CH4 moves to the position of CH1 after 3Δt. Therefore, the light reception signal at CH1, the light reception signal at CH2 after Δt, the light reception signal at CH3 after 2Δt, and the light reception signal at CH4 after 3Δt are the light reception signals for the same part on the inspection surface 4, and the output signal The ratio is S1: S2: S3: S4 = α: β: γ: δ.

Table Therefore, for the same site, obtained four output signals are respectively S1, S2, S3, S4 is output, the output signal S1 = αI, S2 = βI, in S3 = γ I, S4 = δ I One of the output signals S1, S2, S3, S4 is selected as the surface inspection signal.

  As the selected signal, the output signal showing the largest value that does not exceed the proportional limit (measurement limit) L is selected. For example, if the output signals S1 and S2 exceed the proportional limit and the output signal S3 is within the proportional limit, the output signal S3 is selected as the surface inspection signal.

Therefore, the output signal obtained becomes that represented by the sawtooth curve.

Further, S1 = αI, S2 = βI , relative S3 = γ I, S4 = δ I, wound size, if taking the relationship between the size of the foreign object in advance as data, and an output signal S selected The data on the scratches and foreign matters can be obtained immediately by the output value of the signal.

  Thus, with respect to the result of scanning the entire inspection surface 4 with the detection regions CH1, CH2, CH3, CH4, the detection results of the detection region CH1, CH2 after Δt, CH3 after 2Δt, and CH4 after 3Δt, respectively. If the data is selected for the entire inspection area of the inspection surface 4, the surface inspection can be carried out even in the range of the detected light intensity of 0 to I4, and the inspection surface having a large DC component such as a rough surface is obtained. Surface inspection can be performed.

  Thus, in the present invention, the measurement range (dynamic range) is expanded to the detected light intensities I1 to I4. Moreover, it is not necessary to use a special amplifier with the same configuration as the conventional surface inspection apparatus. Further, as the measurement range is expanded, low level noise signals are not exaggerated, and a high S / N ratio can be obtained in the range of detected light intensity of 0 to I4.

  A second embodiment will be described with reference to FIGS.

  The relationship between the laser beam 7 and the detection regions CH1, CH2, CH3, CH4, and the ratio of the detected light intensity are S1: S2: S3: S4 = α: β: γ: δ, and the vertical axis I is detected in the detection region CH1. In this case, the detected light intensity, L, is the same as the first embodiment with respect to the proportional limit (measurement limit) of the detected light intensity I and the output signal level S, the inspection conditions, and the like.

  In the second embodiment, the signal output level is increased in response to an increase in detected light intensity.

  When the output signal of the detection light received in the detection region CH1 and S1 exceed the proportional limit (measurement limit) L, the output signal S2 of the detection light received in the detection region CH2 is selected and received in the detection region CH2. If the detection light output signal and S2 exceed the proportional limit (measurement limit) L, the detection light output signal S3 received in the detection region CH3 is selected, and the detection light output signal received in the detection region CH3. When S3 exceeds the proportional limit (measurement limit) L, the output signal S4 of the detection light received in the detection region CH4 is selected.

  In order to increase the signal output level corresponding to the increase in the detected light intensity, the output signal S2 is added with a deviation ΔS1 from S2 when S1 reaches the proportional limit (measurement limit) L, The output signal is S2 '.

  When the output signal S3 is selected, the deviation .DELTA.S2 from S3 when S2 reaches the proportional limit (measurement limit) L is further added to obtain an output signal S3 '.

  Similarly, when the output signal S4 is selected, the deviation .DELTA.S3 from S4 when S3 reaches the proportional limit (measurement limit) L is further added to obtain the output signal S4 '.

  In the second embodiment, the signal output level increases in response to the increase in the detection light intensity, so that the size of the flaw and the size of the foreign matter can be determined based on the size of the signal output level.

  Also in the second embodiment, the measurement range (dynamic range) is apparently expanded to the detected light intensities I1 to I4. Moreover, it is not necessary to use a special amplifier with the same configuration as the conventional surface inspection apparatus. Also, the noise signal at the low level is not exaggerated.

  Next, FIG. 4 shows a modification of the irradiation light intensity distribution of the laser beam 7.

  This is a case where the irradiation light intensity distribution is a Gaussian distribution having a peak at substantially the center. Also in this example, detection areas CH1, CH2, CH3, and CH4 are set in the irradiation range of the laser beam 7, and the ratio of the detection light intensity to the detection light intensity when light is received in each detection area is obtained in advance. deep. If the inspection is performed in the same manner as in the above embodiment, four inspection signals are obtained for the same part, and the selected signal does not exceed the proportional limit (measurement limit) L, and the output signal indicating the largest value is Selected.

  FIG. 5 shows a laser beam 7 having another different irradiation light intensity distribution.

  The irradiation light intensity distribution shown in FIG. 5 has a trapezoidal distribution without a peak. In this case, even if the detection areas CH1, CH2, CH3, and CH4 are set, no difference in received light intensity occurs between the detection areas, so that each detection area CH1, CH2, CH3, An optical filter is provided in the optical path corresponding to CH4. Alternatively, the amplification factors of the signals from the detection regions CH1, CH2, CH3, and CH4 are made different so that an output difference is electrically generated.

  When an output difference is provided at a required ratio in the output signals from the detection regions CH1, CH2, CH3, and CH4, the inspection can be performed in the same manner as described above.

  FIG. 6 shows a schematic configuration diagram of the signal processing unit 15 of the surface inspection apparatus according to the present invention. The main configuration of the surface inspection apparatus is the same as that shown in FIG.

  In FIG. 6, reference numeral 16 denotes a light receiver 16 used for the side scattered light detector 9.

  The light receiver 16 is an aggregate of light receiving elements such as an area CCD, and each light receiving element individually emits a light receiving signal.

  The light receiving surface of the light receiver 16 is equally divided along the beam feeding direction, and each segment forms detection regions CH1 to CHn. The detection regions CH1 to CHn independently correspond to the detection light intensity. Output signals S1 to Sn (not shown) are output.

  The output signals S1 to Sn are input to the arithmetic unit 17 via amplifiers AM1 to AMn, A / D converters AD1 to ADn, and memories M1 to Mn. The arithmetic unit 17 also includes a signal from a rotational position detector 18 for detecting the rotational position of the silicon wafer 1 (rotational position of the substrate chuck 2) and the radial position of the silicon wafer 1 (in the direction of the substrate chuck 2 feed direction). A signal from the feed position detector 19 for detecting the position) and a clock signal from the clock signal generator 21 are input.

  The arithmetic device 17 is connected to a semiconductor memory device, a memory device 22 such as an HDD, and a display device 23. The memory device 22 receives a program for executing a surface inspection based on the output signals S1 to Sn and an inspection result. A program such as a program that is imaged and displayed on the display device 23 is stored, and data for comparison between the output signal and scratches and foreign matter, or data such as inspection results are stored. A part of the storage device 22 may be allocated to the storage devices M1 to Mn.

  The laser beam 7 is irradiated, and the silicon wafer 1 is rotated while being fed at a constant speed, and the entire inspection surface 4 is scanned by the laser beam 7.

  The light receiver 16 receives scattered light from the irradiated portion of the laser beam 7. The received light is divided into the detection regions CH1 to CHn, and output signals S1 to Sn corresponding to the detected light intensity are output. The detection light intensity is set to be different for each of the detection regions CH1 to CHn. As means for varying the detection light intensity, the irradiation light intensity distribution is changed as described above. Alternatively, the light is optically reduced using a filter or the like. Alternatively, the irradiation light intensity distribution is changed, and the output signals of the detection regions CH1 to CHn are set to a required ratio by optically using a filter or the like.

  The detection areas CH1 to CHn respectively scan the entire inspection surface 4, and the storage devices M1 to Mn receive output signals S1 to Sn from the detection areas CH1 to CHn from the rotational position detector 18, respectively. , And the rotation position is stored in association with the feed position from the feed position detector 19. Therefore, for example, the position on the inspection surface 4 is specified for all signals in the detection region CH1.

  When the arithmetic unit 17 extracts the output signal Sp corresponding to the arbitrary position p on the inspection surface 4 from the output signals S1 to Sn, n signal groups are obtained. One test signal is selected from the n signal groups. As described with reference to FIG. 2, the output signal having the maximum value not exceeding the proportional limit L is selected as the selected signal. It should be noted that the selected output signal is specified where it was stored in the memories M1 to Mn. Therefore, for example, it is determined that the selected signal is one point represented by S2 = .beta.I in FIG. Based on the detected output signal, scratches and foreign matter are determined based on the previously obtained data on the relationship between S2 = βI, the size of the scratch, and the size of the foreign matter, and are stored in the storage device 22 as inspection data. The

  By extracting and selecting the above data for all points on the inspection surface 4, inspection data over the entire inspection surface 4 can be acquired. All the inspection data is stored in the storage device 22, and the inspection result is imaged by the display program and displayed on the display device 23.

  In addition, referring to FIG. 2, the acquisition of inspection data is a surface inspection with a dynamic range that is apparently greatly expanded from 0 to In detected light intensity.

  When the output signals S1 to Sn are associated, the feed rate is Δt between the detection areas CHm and CHm + 1. Therefore, the output signals S1 to Sn recorded in the memories M1 to Mn are associated with time. If data with a time delay of Δt is extracted between the detection regions CHm and CHm + 1, n output signal Sp groups corresponding to the position p can be obtained for an arbitrary position p on the inspection surface 4.

  Since selecting one signal from the output signal group is the same as described above, the description thereof is omitted.

  In the above embodiment, the inspection areas are arranged in a direction orthogonal to the scanning direction, but may be arranged in a direction that coincides with the scanning direction. Alternatively, a plurality of portions may be irradiated with laser beams having different light amounts, and scattered light at each portion may be individually detected. In this case as well, it is only necessary that output signals obtained by detection at each part are associated with each other and a plurality of output signals having different light intensities can be obtained at the same part.

It is explanatory drawing which shows the relationship between the irradiation range of a laser beam and a detection area | region in the 1st Embodiment of this invention, and irradiation light intensity distribution and a detection area | region. It is a figure which shows the relationship between the detection light intensity | strength and output signal level for each detection area | region in 1st Embodiment. It is a figure which shows the relationship between the detection light intensity | strength and output signal level for each detection area | region in 2nd Embodiment. It is explanatory drawing which shows the relationship between the irradiation range and detection area | region of a laser beam in different irradiation light intensity distribution, and irradiation light intensity distribution and a detection area. Furthermore, it is explanatory drawing which shows the relationship between the irradiation range and detection area | region of a laser beam in different irradiation light intensity distribution, and irradiation light intensity distribution and a detection area | region. It is a schematic block diagram about the signal processing part in the surface inspection apparatus which concerns on embodiment of this invention. It is a figure which shows an example of the light receiver used by this invention. It is explanatory drawing which shows schematic structure of a surface inspection apparatus. It is a figure which shows an example of the output signal from the conventional scattered light detector. It is a figure which shows the relationship between the conventional detection light intensity and an output signal level.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Silicon wafer 2 Substrate chuck 3 Motor 4 Inspection surface 5 Inspection light irradiation system 7 Laser beam 9 Side scattered light detector 11 Forward scattered light detector 12 Scattered light 15 Signal processor 16 Light receiver 17 Arithmetic device 18 Rotation position detector 19 Feed position detector 21 Clock signal generator 22 Storage device 23 Display device

Claims (6)

  In a surface inspection method in which a laser beam is irradiated and scanned on an inspection surface to detect foreign matter or the like on the inspection surface, the irradiated portion of the laser beam is divided into a required number of detection regions, and the detected light intensity between the detection regions The required number of output signals with different detection light intensities are acquired for the inspection site, and the output signal indicating the maximum value that is not saturated among the required number of output signals is obtained as a surface inspection signal. Surface inspection method characterized by selecting as   The surface inspection method according to claim 1, wherein the laser beam is irradiated so as to obtain a light intensity distribution in which the light intensity varies at the irradiation site, and a required number of detection regions are set so that the detected light intensity is different.   The surface inspection method according to claim 1, wherein the amount of light is adjusted by an optical filter so that the detection light intensity differs between detection regions.   An inspection light irradiation system for irradiating the inspection surface with a laser beam, a scattered light receiving system for detecting scattered light, and an arithmetic device for performing arithmetic processing for detecting foreign matter based on the scattered light detection output of the scattered light receiving system; The scattered light receiving system divides the laser beam irradiation site into a required number of detection areas, detects the detection light so that the intensity of the scattered light received between the detection areas is different, and the arithmetic unit Is selected as the surface inspection signal from the scattered light detection output that is not saturated among the plurality of scattered light detection outputs obtained for the same part, and configured to inspect foreign matter based on the surface inspection signal. A featured surface inspection device.   The surface inspection apparatus according to claim 4, wherein the inspection light irradiation system irradiates the laser beam so as to obtain a light intensity distribution in which the light intensity changes at an irradiation site, and the inspection region is set to have a different detection light intensity.   The surface inspection apparatus according to claim 4, wherein the scattered light receiving system is provided with an optical filter so that the detection light intensity differs between inspection regions.

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